Gonzaga were unhinged by Toolan's first minute finish into the right corner before they had time to settle into their patterns.

It was set up by hooker Peter Reilly's surge away from a maul and the instinctive work of right wing Sean Lacey in rescuing a move that seemed to falter.

Gonzaga's Ireland Schools centre Daniel Diviney responded by taking the ball on a direct route to draw a penalty for hands in the ruck.

Centre Stephen Murphy found the posts from 40 metres to make it 5-3 after 11 minutes. It was nip and tuck up to the 29th minute when Ross Jones split the posts after the losers' defence drifted offside to make the score 8-3 at the interval.

Gonzaga kept coming forward after the break, one delicious offload from out-half Mark McPhillips almost cracking the cover and Murphy losing the ball forward with room to profit on the outside.

When the southsiders could not break through, Castleknock broke upfield and replacement Niall Cullen forced a penalty on the ground which Jones sent between the posts.